Image forming apparatus

ABSTRACT

An image forming apparatus having a sheet feeding structure for feeding a sheet fed out by a feed-out roller to a pair of resist rollers via a pair of feed rollers, wherein after a leading edge of the sheet comes to the pair of resist rollers, the sheet temporarily curves in a sheet path, between guide members disposed to face to both sides of the sheet. One of the guide members that is disposed downstream from the pair of feed rollers has a convex and a concave. The convex protrudes almost to the normal of the nip portion of the pair of feed rollers. The concave is disposed upstream from the convex with respect to the sheet feeding direction.

This application is based on Japanese Patent Application No. 2009-155375 filed on Jun. 30, 2009, the content of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an image forming apparatus, and more particularly to a sheet feeding structure in an image forming apparatus such as an electrophotographic copying machine.

2. Description of Related Art

In an image forming apparatus such as an electrophotographic copying machine or a printer, a sheet fed out by a feed-out roller is fed to a pair of resist rollers via a pair of feed rollers, and while the pair of resist rollers holds the leading edge of the sheet, the sheet temporarily curves in a sheet path between guide plates disposed to face to both sides of the sheet. This is to correct a possible skew of the sheet and to synchronize the feeding of the sheet with carrying of a toner image to a transfer position.

In the structure wherein a fed-out sheet is temporarily stopped immediately before the pair of resist rollers, when the sheet curves with its leading edge stopped by the pair of resist rollers, the sheet becomes wavy and hits against the guide plates, thereby making a noise. Since a recent copying machine is small, the length between the feed-out roller and the pair of resist rollers via the pair of feed rollers is short. Accordingly, it is likely that the trailing portion of a sheet is still fed by the feed-out roller when the leading edge of a sheet reaches the pair of resist rollers. In this case, if the sheet path defined by the guide plates is tight, when the sheet curves with its leading edge stopped by the pair of resist rollers, the flexure of the sheet cannot be absorbed in the sheet path. Then, the sheet hits against the guide plates strongly and makes a big impact noise.

In order to solve the problem, Japanese Patent Laid-Open Publication No. 2003-252479 teaches that elastic members, that is, resin films are provided for guide members located upstream from the pair of resist rollers with respect to a sheet feeding direction. This way of solving the problem is to distribute the impact of the sheet. In this way, however, a multiple of resin films are required, and the number of necessary components increases.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an image forming apparatus having a structure for suppressing an impact noise that occurs when a sheet is stopped by a pair of resist rollers.

According to an aspect of the present invention, an image forming apparatus comprises a sheet feeding structure for feeding a sheet fed out by a feed-out roller to a pair of resist rollers via a pair of feed rollers, wherein after a leading edge of the sheet comes to the pair of resist rollers, the sheet temporarily curves in a sheet path, between guide members disposed to face to both sides of the sheet, wherein one of the guide members that is disposed downstream from the pair of feed rollers with respect to a sheet feeding direction has a convex and a concave; wherein the convex protrudes substantially to a normal of a nip portion of the pair of feed rollers; and wherein the concave is disposed upstream from the convex with respect to the sheet feeding direction.

BRIEF DESCRIPTION OF THE DRAWINGS

This and other objects and features of the present invention will be apparent from the following description with reference to the accompanying drawings, in which:

FIG. 1 is a schematic view of an image forming apparatus according to an embodiment of the present invention;

FIG. 2 is a sectional view of a sheet feeding structure provided in the image forming apparatus, the sheet feeding structure being located between a sheet feed cassette and a pair of resist rollers;

FIG. 3 is an illustration of a first example of the sheet feeding structure;

FIG. 4 is an illustration of a second example of the sheet feeding structure;

FIG. 5 is an illustration showing a state wherein a sheet is fed in the first example of the sheet feeding structure;

FIG. 6 is an illustration showing a state wherein a sheet is resisted by the pair of resist rollers; and

FIG. 7 is an illustration showing a state wherein a sheet is fed in a comparative example.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An image forming apparatus according to an embodiment of the present invention is hereinafter described with reference to the accompanying drawings. In the drawings, the same members and parts are provided with the same reference symbols, and repetitions of the same descriptions are omitted.

An image forming apparatus according to an embodiment of the present invention is described with reference to FIG. 1. The image forming apparatus is a tandem type color printer. The printer mainly comprises process units 110 (110 y, 110 m, 110 c and 110 k) for forming toner images of yellow (Y), magenta (M), cyan (C) and black (K) respectively, a laser scanning unit 120 and an intermediate transfer unit 130.

Each of the process units 110 comprises, in a housing shown by the dotted line in FIG. 1, a photosensitive drum 112, a charging roller 113, a developing device 114, a residual toner/charge cleaner, etc., and is capable of sliding in a direction perpendicular to the paper surface of FIG. 1 so as to be detachable from the body of the printer. In each of the process units 110, an electrostatic latent image is formed on the photosensitive drum 112 by laser radiation from the laser scanning unit 120, and the electrostatic latent image is developed into a toner image.

The intermediate transfer unit 130 has an intermediate transfer belt 131 that is an endless belt driven to rotate in a direction “B”. Electric fields are formed by transfer rollers 132 located opposite to the respective photosensitive drums 112, and thereby, the toner images formed on the photosensitive drums 112 are transferred to the intermediate transfer belt 131 and combined thereon (first transfer). Such an electrophotographic image forming process is well known, and a detailed description thereof is omitted.

An automatic sheet feed unit 40 for feeding sheets one by one is provided in a lower part of the printer body. Each sheet is fed from a feed-out roller 11 to a pair of resist rollers 15 and then, to a nip portion between the intermediate transfer belt 131 and a second transfer roller 135, where the toner image (the color composite image) is transferred to the sheet (second transfer). Thereafter, the sheet is fed to a fixing unit 145, where a heating treatment is performed, and is ejected on a tray 146 located on an upper surface of the printer body.

The image forming apparatus has a characteristic sheet feeding structure that forms a sheet path between the feed-out roller 11 and the pair of resist rollers 15 as shown by FIG. 2. The other components of the image forming apparatus are the same as those of conventional electrophotographic copying machines and printers.

The sheet feeding structure comprises a feed-out roller 11 and a separation roller 12 that are disposed at an outlet of the feed unit 40, a pair of feed rollers 13, and a pair of resist rollers 15. The sheet feeding structure feeds a sheet upward in FIG. 2. Further, guide plates 21-28 and a resin film 29 are disposed around the rollers.

The guide plate 23 is disposed in a position downstream from the pair of feed rollers 13 and in the side opposite to the feed-out roller 11. The guide plate 23 has a convex 23 a and a concave 23 b. The top of the convex 23 a reaches the normal “H” (see FIG. 3) of the nip portion of the pair of feed rollers 13. The concave 23 b is located upstream from the convex 23 a with respect to the sheet feeding direction.

FIG. 3 shows a first example. The convex 23 a and the concave 23 b extend horizontally to cover the entire width of a sheet. FIG. 4 shows a second example. The convex 23 a that protrudes to the normal “H” of the nip portion of the pair of feed rollers 13 may be ribbed.

In the structure, with rotation of the feed-out roller 11, a plurality of sheets stacked in the feed unit 40 are fed out in the upper right direction in FIG. 3, one by one starting with the uppermost sheet. The fed-out sheet is fed upward (along the normal “H”) by the pair of feed rollers 13 to the pair of resist rollers 15, guided by the guide plates 21-28 and the resin film 29. Meanwhile, the pair of resist rollers 15 stops, while the pair of feed rollers 13 is continuously rotating. Therefore, when the leading edge of the sheet comes to the pair of resist rollers 15, the sheet starts bending around the pair of feed rollers 13. Then, the sheet curves in the sheet path. Thereafter, the pair of resist rollers 15 is driven to rotate at a time to synchronize the sheet with a toner image at the transfer section immediately above the resist rollers 15. Thereby, the sheet feeding is resumed.

The pair of resist rollers 15 is positioned leftward from the normal “H”, and the upper portion 23 d of the guide plate 23 curves leftward. Therefore, when a sheet is fed from the pair of feed rollers 13 toward the pair of resist rollers 15 in the normal direction “H”, the sheet collides with the upper portion 23 d and tends to lean against the guide plate 23. In this embodiment, however, since the guide plate 23 has a convex 23 a and a concave 23 b as shown by FIG. 5, the sheet is fed with a space “Q” from the guide plate 23 without leaning against the guide plate 23. When the leading edge of the sheet comes to the pair of resist rollers 15, whereby the sheet starts curving, the flexure is absorbed by the space “Q” as shown by FIG. 6. Consequently, the impact noise caused by a hit of the sheet against the guide plate 23 can be suppressed.

For comparison, FIG. 7 shows a sheet that is fed in a comparative example wherein the guide plate 23 does not have a convex. The sheet is fed to the pair of resist rollers 15 in a tight sheet path while leaning against the guide plate 23. When the leading edge of the sheet comes to the pair of resist rollers 15, whereby the sheet starts curving, there is no space to absorb the flexure of the sheet. Therefore, the impact of the curving sheet influences the guide plate 23 entirely, and a big impact noise occurs.

When a sheet reaches the pair of resist rollers 15, the sheet starts curving, and more specifically, first, the lower portion near the pair of feed rollers 13 starts curving. Therefore, the convex 23 a of the guide plate 23 is formed preferably in such a way to meet the condition that the distance between the pair of feed rollers 13 and the top of the convex 23 a is smaller than (½)L and is greater than (¼)L, wherein L is the distance between the pair of feed rollers 13 and the pair of resist rollers 15.

If the protrusion of the convex 23 a into the sheet path is too large, the convex 23 a may block the sheet feeding. If the protrusion of the convex 23 a is too small, the space “Q” is small, and the effect of suppressing the impact noise may be unsatisfactory. Accordingly, it is the best that the top of the convex 23 a is almost on the normal “H” of the nip portion of the pair of feed rollers 13.

The operation and the effect of the first example shown by FIG. 3 have been described. The second example shown by FIG. 4 has the same operation and effect as those of the first example.

OTHER EMBODIMENTS

The positional relationship between the feed-out roller, the pair of feed rollers and the pair of resist rollers may be arbitrarily designed. Further, various guide members may be disposed arbitrarily.

Although the present invention has been described with reference to the accompanying drawings, it is to be noted that various changes and modifications are possible to those who are skilled in the art. Such changes and modifications are to be understood as being within the scope of the present invention. 

1. An image forming apparatus comprising a sheet feeding structure for feeding a sheet fed out by a feed-out roller to a pair of resist rollers via a pair of feed rollers, wherein after a leading edge of the sheet comes to the pair of resist rollers, the sheet temporarily curves in a sheet path, between guide members disposed to face to both sides of the sheet, wherein one of the guide members that is disposed downstream from the pair of feed rollers with respect to a sheet feeding direction has a convex and a concave; wherein the convex protrudes substantially to a normal of a nip portion of the pair of feed rollers; and wherein the concave is disposed upstream from the convex with respect to the sheet feeding direction.
 2. An image forming apparatus according to claim 1, wherein the convex is formed such that a top of the convex is located downstream from the pair of feed rollers with respect to the sheet feeding direction at a distance smaller than (½)L and greater than (¼)L, wherein L is a distance between the pair of feed rollers and the pair of resist rollers.
 3. An image forming apparatus according to claim 1, wherein the guide member having the concave and the convex is disposed in an opposite side of the feed-out roller. 